<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>重复请求问题</title>
</head>
<body>
    <button>点击发送</button>
    <!-- <button>点击取消</button> -->
    <script>
        //获取元素对象
        const btns = document.querySelectorAll('button');
        let x= null;
        //标识变量
        let isSending = false; //是否正在发送AJAX请求
        btns[0].onclick = function() {
            //判断标识变量
            if(isSending) x.abort();  //若正在发送，则取消该请求，创建一个新的请求
            x = new XMLHttpRequest();
            //修改 标识变量的值
            isSending = true;
            x.open("GET",'http://127.0.0.1:8000/delay');
            x.send();
            x.onreadystatechange = function() {
                if(x.readyState === 4) {
                    //修改标识变量
                    isSending = false;
                }
            }
        }

       
    </script>
</body>
</html>